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Neopanamax beam is just under 52m, with a height of just under 60m. Let's give it about 50% margins on each side, and that give you 100m between bridge supports. A suspension bridge with a 100m span would not appear on a list of notably long bridges in our world.

Suddenly this is not looking like a huge technological problem.

I suggest that you run two 6-wide bridges next to each other, one for heavy trains and the other for your metro trains and vehicle traffic. You might be interested in reading https://www.researchgate.net/publication/330482896_Live_Load_Spectra_for_Railway_Bridges_in_USA
which discusses actual loading parameters.